help! single click is opening groups instead of just selecting - whats happened?
Does it cause double-click behavior in general or only in SketchUp?
Mouse buttons can wear off and cause vibrations that trigger twice within a short time interval. Then when you move your finger once the operating system registers a double-click. If that is the case, check whether your operating system or mouse driver has a setting to increase the minimum time until an input event is interpreted as double-click. Or you may search on the internet for an aplication that filters or debounces mistriggers (like MouseFix").
On Windows, … Start Menu > Control Panel > Mouse